Rotary heat exchangers or rotary regenerative heat exchange apparatus of axial flow type and in which a heat exchange wheel rotates in a plane and within a wheel housing providing almost 180.degree. sectors for inlet and outlet flow paths for gasses present difficulties in sealing between adjacent opposed side surfaces of the rotating heat exchange wheel and faces of the housing pillars which define the almost 180.degree. sectors of the inlet and outlet flow paths. Leakage of gasses from the outlet path to the inlet path tend to occur because of the high temperature of the outlet path and relatively higher pressure therein as compared to the cooler gasses and lower pressure in the inlet path. Any leakage of gasses between wheel housing surfaces and rotary wheel surfaces reduces the efficiency and effectiveness of the heat exchange function. Outlet or discharge gasses from a fume incinerator or burner means, which are passed through the outlet flow path, heat the heat exchange material of a sector of the rotary wheel before discharge of the outlet gasses into a waste stack. The heated exchange material of that sector of the wheel upon rotation to the inlet path side of the housing will be in heated condition to exchange heat to the cooler inlet gasses. The cooler inlet gasses will absorb heat from that sector of the rotary wheel which has just been rotated from the outlet path to pre-heat the inlet gasses before feeding into an incinerator, furnace or other heating means.
It will be apparent that a rotary heat exchange wheel rotating as above described will be subject to expansion and contraction both axially, radially and circumferentially due to its metallic design. Sealing between adjacent surfaces of the wheel and wheel housing and between the inlet and outlet paths to prevent passage of gasses or a substantial restriction of such leakage flow presents numerous problems because of the variable stressing of the wheel and its reaction to widely varying temperatures in relatively short time cycles. For example, at the cool side face of the rotary wheel, gasses may enter the inlet passage at an ambient temperature of 70.degree. F. On the hot outlet side of the rotary wheel, the temperatures of the gasses after burning and approaching the wheel may be as high as 1,400.degree. F or more. The response or reaction of the wheel structure and wheel housing to such a thermal differential range within its 360.degree. circumference creates repetitive thermal stresses of expansion and contraction in the wheel and wheel housing components which render sealing and the effective efficient operation of the rotary heat exchange apparatus difficult.
Prior proposed heat exchange rotary wheel constructions have included various means for preventing passage or leakage of gasses between adjacent surfaces of the wheel housing and the rotary wheel. Prior examples of such sealing means include a peripheral inwardly extending rib on the wheel housing for engagement with sealing material such as felt carried on the outer circumferential edge face of the wheel in a humidity changer for air conditioning (U.S. Pat. No. 3,398,510). Interleaved flanges and ribs on a horizontally disposed wheel at the top circumferential edges of the wheel and housing is shown in U.S. Pat. No. 2,744,731. Circumferential rim seals of a flexible flange type are shown in U.S. Pat. No. 3,482,622 and packing elements at the circumferential rim are shown in U.S. Pat. No. 4,062,129. Various other prior proposed constructions have been used for preventing leakage through clearance openings between a wheel housing and the enclosed rotating wheel.
In a hot-cool temperature environment as generally mentioned above for the rotary heat exchange wheel of the present invention, the rotary wheel is subjected to varying repetitive expansion and contraction as each sector thereof moves from the discharge path in which the hot side of the wheel may be subject to temperatures in the order of 1,400.degree. or more to the cool side of the wheel where at the inlet path temperatures may be ambient such as 70.degree. F. While the wheel rotates relatively slowly, for example 16 RPM, it will be readily apparent that thermal stresses imposed upon the wheel structure cause expansion and contraction of wheel components axially, radially, and circumferentially. Complete sealing of leakage areas around the periphery of the wheel and at the hub of the wheel is difficult because of the thermal conditions. Moreover, on the hot side face of the wheel, the pressure differential between the inlet path and the outlet path may vary up to one to six inches of water column and, therefore, leakage flow would occur from the high pressure side to the low pressure side. Such leakage flow lessens and detracts from efficient use of the wheel heat exchange material which is to absorb as much heat as possible from the outlet path as the wheel sectors pass through the outlet path and then transfer to the inlet gas flow such absorbed heat at the inlet path so that the inlet flow of gasses will be pre-heated. The fuel cost of operation of the burner or incinerator means is effectively reduced by supplying pre-heated gas or air.